Method of producing silver oxide and nickel containing electrodes for electric batteries

ABSTRACT

Silver oxide electrodes for electric batteries, particularly primary batteries capable of delivering a high-temporary current output, are produced by compressing a mixture of 10 to 40 percent by weight of pulverulent silver oxide and 60 to 90 percent of pulverulent nickel, and hard-pressing the resulting compressed layer onto a carrier structure, preferably of copper or silver, at pressures of about 0.5 to about 1.4 t/cm.2 in an oxidizing or inert atmosphere at a hot-pressing temperature below the dissociation temperature of the silver oxide, this temperature being generally between about 100* and about 300* C.

United States Patent Inventors Dietrich Berndt Kronberg; Walter K. Lux,Garchlng an der All; Kurt Weidlnger, Frledrichsdorf, all of GermanyAppl. No. 54,839 Filed July 14, 1970 Patented Dec. 28, 1971 AssigneeVarta Aktiengesellschalt Frankfurt am Main, Germany Priority Aug. 5,1969 Germany P 19 39 713.8

METHOD OF PRODUCING SILVER OXIDE AND NICKEL CONTAINING ELECTRODES FORELECTRIC BATTERIES 6 Claims, No Drawings U.S. Cl 136/20, 136/120 Int. ClH01m 13/00 Field 01 Search 136/20, 21,

[56] References Cited UNITED STATES PATENTS 2,830,108 4/1958 Peters136/20 3,104,990 9/1963 Solomon et al. 136/20 3,230,114 1/1966 Friese eta1. 136/120X 3,276,975 10/1966 I-Iolechek 136/20 X 3,389,019 6/1968 Biro136/120 Primary Examiner-A. Skapars Attorneys-Curt M. Avery, Arthur E.Wilfond, Herbert L.

Lerner and Daniel J. Tick METHOD OF PRODUCING SILVER OXIDE AND NICKELCONTAINING ELECTRODES FOR ELECTRIC BATTERIES Our invention relates to amethod of producing silver oxide electrodes for electric batteries bycompressing a mixture of silver oxide powder and nickel powder andnickel powder. In a preferred though not exclusive aspect the inventionparticularly concerns primary batteries that are to be used undertemporarily high electric load conditions.

Electrodes containing silver .oxide as an electrochemically active massare produced, as a rule, by converting a loose structure of elementalsilver into silver oxide by subjecting the structure to a formationtreatment.

In such production methods, silver powder may directly be sintered, orthe starting material may consist of silver oxide which is deposited asa paste upon a carrier structure. The mass is then heated and thusthermally converted to sintered elemental silver powder and isultimately subjected to afterpressing. Electrodes produced from silveroxide in this manner can be more readily and more satisfactorilyconverted by the forming treatment, so that the resulting electrodes, asa rule, comprise a sinter skeleton which, in most cases, contains a gridstructure of silver stretch meal for mechanical reenforcement and as anelectric current conductor. For formation of such electrodes, they areanodically oxidized in alkaline solutions. Thus, an oxidation degree ofAgO to AgO is attained. Hence, the current delivering capacity(measured, for example, in ma./h.) of such electrodes is lower than thatof electrodes which contain pure AgO. Besides, the formationtreatedelectrodes are often found to retain alkali remainders whichdetrimentally affect the storage ability. The production of suchelectrodes is expensive and time consuming.

Silver oxide electrodes with better electrochemical properties, althoughof only very slight mechanical strength, can also be produced directlyfrom silver oxide (preferably silver Il-oxide) either by dry prepressingunder high pressure or from a paste of water and silver oxide. A highermechanical strength of such electrodes can be attained by adding organicbinding agents.

For special purposes, there is a demand for primary elements andbatteries that are capable of delivering for a short interval of time,such as several seconds up to several minutes, a very high amount ofelectric current at a relatively uniform voltage level. Such batteriesare to be applicable down to low ambient temperatures and, particularly,are to remain storable for prolonged periods of time.

Attempts to meet these severe demands with the aid of activatablesilver-zinc batteries, have shown that sintered and formation-treatedsilver oxide electrodes that possess a sufficient mechanical strengthmust contain a multiple of the silver oxide quantity needed forordinary, less exacting requirements. On the other hand, silver oxidepressed electrodes with organic binding agents are not suitable if itmust be possible to heat the electrolyte as well as the electrode platesof the activatable battery, because the mixture of oxidizing agent andoxidizable substance present in such batteries may cause an explosivedecomposition of the battery.

For these reasons, the above-mentioned requirements with respect totemporary high loadability and prolonged storability make nickel powderparticularly well suitable as a binding agent for the electrodes. Suchuse of nickel powder as a binder in silver electrodes is known per se,for example from the German Pat. No. 946,071. In this patent it isproposed to produce a silver-containing positive electrode by sinteringa mixture of nickel powder with silver powder or pulverized silvercompounds. Only slight quantities of nickel powder, to act as a bindingagent, are employed and the sintering is effected at the conventionalhigh sinter temperatures of about 700 to 900 C. For attaining a highactivity of such an electrode, a formation is needed by means of which,however, no optimum of the oxidation degree of the silver oxide can besecured.

It is an object of our invention to produce a silver oxide electrodesuitable for the above-mentioned uses requiring a high temporaryelectrical loadability as well as satisfactory storageability, whilealso avoiding the above-mentioned disadvantages of the known silveroxide electrodes.

To this end, and in accordance with our invention, we produce silveroxide electrodes for electric batteries by compressing into the shape ofa layer a mixture of 10 to 40 percent by weight of silver oxide powderand 60 to 90 percent of nickel powder, and we then hot-press theresulting layer onto a carrier structure at a pressure of about 0.5 toabout 1.4 t/cm in an oxidizing or inert atmosphere at a hot-pressingtemperature below the dissociation temperature of the silver oxide.

When using silver (ID-oxide powder, the hot-pressing temperature is keptpreferably between about 100 and 110 C. When using silver (l)-oxide, thetemperature of the hotpressing operation may be in the range of about100 to about 300 C. and is preferably between 250 and 300 C.

Suitable as carrier of the pressed body are particularly silver-platedor nickel-plated and perforated copper sheets, also grid or meshstructures of copper or copper stretch metal. Likewise suitable ascarrier structure is perforated silver sheet material, silver mesh orgrid structure, or silver stretch metal.

The hot pressing operation may be performed in air or in a nitrogenatmosphere. Particularly well suitable as pulverulent silver for theprocesses according to the invention are chemically produced silveroxide powders. Preferably employed as nickel powder for the purpose ofthe invention is pulverulent nickel made by the carbonyl process andhaving a low bulk density.

In the following, the method according to the invention will be furtherillustrated with reference to a specific example.

EXAMPLE Twenty-five g. of chemically produced silver (l)-oxide wereintimately mixed with g. nickel powder having a bulk density of about0.55 g./ml. For producing electrode plates (64 47Xmm.), the mixture wasconverted to the shape of layers, each having a rectangular size of 6447 mm. and each consisting of 3.5 g. of the mixed mass. Some of thelayers were made by pressing the mixture in moulds under a pressure of0.8 t/cm. others were made by rolling with a gap of 0.2 mm. betweenrollers having a roller diameter of mm.

The layers made in this manner are sufficiently strong andself-supporting for the further fabrication.

Two such layers were placed into a hot-pressing mold together with aninterposed current conductor of perforated and silver-coated coppersheet material. The mold was heated in a furnace under a nitrogenatmosphere to 250 C. and at this temperature was compressed at apressure of l t/cm.

These electrodes, at normal room temperature (about 70 C.) and a surfaceloading of 150 ma./cm. exhibited a current delivering capacity of about250 ma.-hr.

Advantageously applicable as counter-electrodes are zinc electrodes ofthe same size consisting of fine zinc foil. These are first defattedwith trichlorethylene and then superficially etched in 5 percenthydrochloric acid for a period of 5 to 10 minutes.

Upon a study of this disclosure it will be apparent to those skilled inthe art, that our invention permits of various modifications and hencemay be embodied in specific methods and resulting products other thanthose particularly described herein, without departing from theessential features of the invention, and within the scope of the claimsannexed hereto.

We claim:

1. The method of producing silver oxide electrodes for electricbatteries, such as temporarily highly loadable primary batteries, whichcomprises compressing and forming layer from a mixture of 10 to 40percent by weight of pulverulent silver oxide and 60 to percent ofpulverulent nickel, and hotpressing the resulting layer onto a carrierat pressures of about 0.5 to about 1.4 t/cm. in an oxidizing or inertatmosphere at a hot-pressing temperature between about and about 300formed substantially of copper or silver.

5. The method according to claim 1, wherein the carrier is formed ofnickel-plated copper.

6. The method according to claim 1, wherein the carrier is formed ofnickel-coated copper stretch metal.

2. The method according to claim 1 wherein the pulverulent silver oxideis silver (II)-oxide, and the hot-pressing temperature is between 100*and 110* C.
 3. The method according to claim 1 wherein the pulverulentsilver oxide is silver (II)-oxide, and the hot-pressing temperature isbetween 250* and 300* C.
 4. The method according to claim 1, wherein thecarrier is formed substantially of copper or silver.
 5. The methodaccording to claim 1, wherein the carrier is formed of nickel-platedcopper.
 6. The method according to claim 1, wherein the carrier isformed of nickel-coated copper stretch metal.